Telephone trunking system



Nov. 17,1942. v H. w. ULRICH I 3 15 TELEPHONE TRUNKING SYSTEM Filed July 26. 1941 3 Sheets-Sheet l OPERATOR I ia- FIG. 4

FIG 3 OPERATOR INVENTOR H. W. UL RICH ATTOQNFV Nov. 17,1942. w, UL I 2,302,587

TELEPHONE TRIENKING SYSTEM Filed July 26, 1941 3 Sheets-Sheet 2 v gllwwvf l /6 v POLARIZED DIAL INVENTOP H. W. ULRICH A r TORNEV Patented Nov. 17, 1942 r TELEPHONE TRUNKING SYSTEM Horace W. Ulrich, Newark, N. J assignor to Bell Telephone Laboratories, Incorporated, New York, N. I, a corporation of New York Application July 26, 1941, Serial No. 404,101

solaims. (01. 179-27) This invention relates to telephone exchange systems and more particularly to arrangements atan operators position intermediate an incoming trunk from a calling exchange and an outgoing trunk terminating at an automatic central oifice, at which operators position, subsequent to connection of the incoming trunk to the outgoing trunk, the intermediate operator associates an impulse device with the outgoingtrunk to control the extension of the trunk through the automatic ofiice to a called subscriber.

l A feature of the invention resides in a trunk extending from a so-called master ofl'ice to a link type community dial exchange which dial exchange is arranged to reverse the normal polarity of the trunk battery thereat immediately upon seizure of, the trunk at the master office by an incoming trunk from a distant calling exchange and to maintain this condition until an idle link is available and connects itself to the trunk whereupon the polarity of the battery is restored to its normal condition which restoration of normal battery polarity is effective, in case a dial cord is associated with thetrunk, to light a lamp before the operator as a signal to commence dialing and to prevent suchreversals from transmitting supervisory signals back over the. incoming trunk until the dial cord has been disconnected whereupon a subsequent reversal caused by the called subscriber removinghis receiver from the hook will transmit a signal to.

the calling exchange in the usual manner.

The invention will be understood from the following description when read in connection with the accompanying drawings which repre sent anarrangement of circuits embodying the invention.

Referring to the drawings,

Fig. 1 represents the incoming end of the trunk circuit from a distant calling exchange terminating at a so-called master office operatorsv position Fig. 2 represents the master ofi'ice end of. a

trunk circuit extending to a community dial automatic exchange; ,y

Fig. 3 represents a dial cord for associationwith a community dial trunk to control automatic switching equipment thereover;

- Fig. 4 representsa conventional operators cord Fig. 5 represents the circuit arrangement of the community dial ofiice.

relay 4 and at its contact l9 short-circuits the Following is a description of the operation of the circuits of the invention.

Let it first be assumed that a call is originated at a distant exchange, not shown, over the trunk line T of Fig. l for a subscriber A reached through-the community dial exchange (Fig. 5).

Connection to the trunk T at the distant calling exchange causes the master office operators telephone set- (not shown) to be connected thereto in the usual manner. When the operator is connected and learns that a subscriber A in the community dial exchange of Fig. 5 is wanted, she

inserts plug I of the trunk in the out jack 2 of the community dial trunk whereupon relay 3 in the incoming trunk and sleeve relay 4 of the community dial trunk operate. Operation of relay 3 closes its contact 5 thereby completing a circuit to operate relay 6 of the community dial trunk, when the tip and ring contacts of the plugs are both in engagement with the respective tip and ring springs of jack 2. This circuit can be traced from battery, lower right winding of repeating coil 8, winding of relay I, ring contacts of the plug and jack, winding of relay 6, contacts 9 of relay l0, tip contacts of the jack and plug, contacts 5 of relay 3, upper right winding'of coil 8 to ground. Relay 6 operates in this circuit and in conjunction with relay 4 causes operation of relay I2 in .the following circuit, battery, contacts l3 of relay 6, conductors l4 and I5, lower left winding of repeating coil l6, contacts l1 and winding of relay I2 to ground at contacts of sleeve relay 4. Operation of relay l2 in this circuit closes a locking circuit for itself at its contacts l8 under control .of the sleeve lower (high resistance) winding of polarized relay 20, thereby causing operation of line relays 2| and Met the dial oflice (Fig. 5). The circuit for relays 2| and 22 can be traced from battery, winding of relay 22, contacts 23 of relay 24, lower left winding of repeating coil 25, ring conductor of trunk DT, contacts26 of relay 21, lower right winding of coil l6, contacts I9 of relay I2, upper (low resistance) Winding of relay 20, upper right "winding of coil l6, contacts 28 of relay 21, tip

conductor of the trunk DT, upper left winding of coil 25, contacts 29 of relay 24, and winding of relay 2| to ground.

Operation of relay 2| closes its lower contact,

thereby connecting battery through inductance 30 to the tip conductor 3i to ground over contacts 32 of cut-ofi relay 33 and the right-hand winding of line relay 34 which relay operates in this circuit and closes its contact 35 to connect ground to start lead 36 to cause a line finder to hunt for the calling trunk. Operation of relay 2| also operates relay 3'! which in turn closes an obvious circuit to operate reversing relay 24 from ground at contacts 36 of relay 39. Operation of relay 24 reverses the direction of the current flowing in polar relay 26 at the master oflice (Fig. 2) which relay then moves its grounded armatures to close contacts 46 thereby operating relay 4| to close, at its contacts 42, one break in the supervisory bridge across the condenser 43 at the mid-point of the left side of repeating coil l6 which circuit is, however, now open at contacts 44 of relay Ill, which relay operated in response to operation of relay |2 following opera-- tion of relay 6. The circuit for relay l6 can'be traced from battery, winding of relay l0, contacts 45 of relay 6, and conductor 46 toground at con-' tacts 41 of relay I2. Relay ID in operating looks over its contacts 48 to ground on conductor 46.

Relay H3 in operating also opens its contacts 9 to release relay 6 thereby completing at contacts 3 a connection between the incoming trunk T and the left side of the repeating coil I6.

When a line finder at the dial office finds the calling line it connects ground, over the sleeve terminal of the finder bank, to sleeve conductor 49 thereby operating relay 39 which opens its contact 38 to release relay 24 thereby restoring the original polarity of the trunk battery which causes the armature of polar relay 26 to move into engagement with contact 50 and to open its contacts 46 thereby releasing relay 4| which reconnects ground at its uppermost contacts to prepare relay 21 for operation under control of the dial cord DC (Fig. 3) which is adapted to be connected to the dial jack At the time the operator connects trunk plug I to jack 2, or subsequent thereto, she also inserts plug 52 of the dial cord DC into dial jack 5| and if a line finder at the dial oflice has already attached itself to the trunk, thereby restoring the trunk battery to its normal polarity to cause relay 4| to release, relay 53 will operate in a circuit from battery,.high resistance upper and low resistance bottom winding of relay 53 in series, sleeve contacts of the plug and jack, winding of relay 2'! to ground at the uppermost contacts of relay 4|. Operation of relay .53 causes pilot lamp 54 to become. lighted as a signal to the operator that a line finder is attached to the trunk at the dial ofiice and that the equipment thereat is in readiness toreceive dial pulses. Relay 2'! does not operate at this time due to the combined resistance of the upper and lower windings of relay 53 and consequently relay 55 operates in parallel with polar relay 20 from battery on the tip and ring of trunk DT supplied at the dial office, the circuit for which can be traced from the tip conductor of trunk DT, upper winding of relay 55, conductor 66, tip of the dial jack 5|, and plug 52, normally closed pulsing contacts 62 of the dial D, impedance 59, ring contacts of plug 52 and jack 5|, conductor 6| and lower winding of relay 55 to the ring conductor of the trunk to the dial ofiice. Operation of relay 55 closes its contacts thereby operating relays 63 and 64 from ground at contacts 56 of relay 26. Relay 63 looks over its lower contacts to ground at contacts 41 of relay l2 and at its contact 65 short-circuits the open contacts 44 of relay ID.

In case there are no links available at the dial ofiice, i. e., the line finders are all busy, relay 24' of the dial office will remain operated to -hold 78- the trunk battery reversed, thereby holding relay 4| operated and when the dial cord is connected, relay 53 will not operate and lamp 54 will remain dark.

Assuming, however, that a link at the dial oifice is available and has attached itself to the trunk and the dial cord is plugged into jack 5|, the operator is notified by the lighting of pilot lamp 54 that she can start dialing, When the operator moves the dial ofi normal, for the first series of pulses, the off-normal contacts 56 are closed thereby operating relay 51 which in turn operates relay58. Relay 51 in operating shortcircuits the upper high resistance winding of relay 53 thereby reducing the resistance of the sleeve circuit including relay 2! which relay then operates to disconnect the repeating coil I6 and relay 20 from the dial trunk, to short-circuit relay 55, and to connect conductors and 6| to the trunk leading to the dial office. The pulsing circuit is now complete from the dial through to the distant dial ofiice. Relay 55 now being released, relay 64 releases thereby reclosing its contacts whereby the supervisory bridge is now only open at contacts 42 of relay 4|. Each time the dial returns to normal, relay 2| releases whereupon relay 55 operates to again operate relay 64 which introduces another break in the supervisory bridge. At the conclusion of the dialing operation, the operator removes the plug of the dial cord from jack 5| whereupon relay 55 releases in turn releasing relay 64 thus placing the supervisory bridge under the exclusive control of relay 4|. When the called subscriber answers, the battery at the dial ofiice is again reversed in the usual manner, polar relay 20 at the master office again moves its armature to open contacts 50 and close contacts 40, thereby operating relay 4| which closes its contacts 42 thereby completing, for the first time, the circuit of the supervisory bridge across the midpoint of the left side of repeating coil |6 whereupon a circuit is closed to operate relay 1 in the calling trunk T (Fig. 1) which can be traced from battery, lower right winding of repeating coil- 8, winding of relay 1, ring contacts of plug" and jack 2, contact 61 of relay |0, upper backcontact of relay 6, conductors I4 and I5, lower left winding of repeating coil l6, contacts 68 of relay |-2, contacts 42 of relay 4|, resistance '69, upper contacts of'relay 64, contacts of relay 63, upper left winding of coil l6, conductors l6 and 1|, contacts 12 of relay 1!), tip contacts of jack 2 and plug contacts 5 of relay '3, upper right winding of coil 8, to ground;

Operation of relay 1 short-circuits the righthand high resistance winding of the line relay 66 thereby causing a supervisory signal at the distant calling exchange to be extinguished, in a Well-known manner, to indicate to the operator thereat that the called subscriber has answered.

When the conversation is finished and the called subscriber restores his receiver to the hook the battery at the dial office is restored to normal polarity and relay 20 moves itsxarmature to open contacts 40 thereby reelasing relay 4| which opens at its contacts 42the circuit, previously traced, for operating relay 1 in the calling trunk T. Release of relay 4| removes the short circuit around the right-hand Windingrof relay 66 which thereby increases the resistance of the bridge across the trunk T and causes the supervisory signal at the calling exchange to be displayed."

When the operator at the ,calling exchange di'sconnects from the trunk, a disconnect signal (not shown) at the master oflice is displayed as an indication that plug I may be removed from jack 2. When this is done all relays restore and the circuit returns to normal.

Calls from the dial exchange over .dial oflice trunk DT cause the trunk circuit at the master oifice to function in a well-known manner to light the line lamp 173 which call is answered in the usual manner by connecting the cord circuit C (Fig. 4) to the inward jack Hi.

What is claimed is:

1. In a telephone system, a calling exchange, an automatic exchange having incoming trunk finder switches thereat, an intermediate dialing operators position, a trunk between the calling exchange and the operators position and a trunk between the operators position and the automatic exchange, a dial at the operators position, a signal device associated with said'dial, switching means for connecting the calling exchange trunk to the automatic exchange trunk, means independent of said switching means for connecting said dial to said automatic exchange trunk, said automatic exchange being arranged to reverse the polarity of the battery connected to the incoming trunk when it is connected to the calling trunk at the operators position, to restore the normal polarity of the battery when a trunk finder switch is connected thereto, and to again reverse the battery supply polarity when the called subscriber answers, means at the operators position responsive to said second reversal to actuate said signal device when the dial. is connected to the'automatic exchange trunk as an indication to the operator that the automatic exchange is conditioned to receive dial pulses, means for transmitting supervisory signals over said calling exchange trunk responsive to a reversed polarity of the automatic exchange trunk battery and other means to prevent transmission of supervisory signals over said calling exchange trunk until said dial has been connected to and disconnected from said automatic exchange trunk.

2. In a telephone system, a calling exchange, 'an' automatic exchange having incoming trunk finder switches thereat, an intermediate operators position, a trunk between the calling exchange and the operators position, a trunk between the operators position and the automatic exchange, a dial at the operators position, a signal device associated with said dial, switching means for connecting the calling exchange trunk to the automatic exchange trunk, means independent of said switching means for connecting said dial to said automatic exchange trunk, said automatic exchange being arranged to reverse the normal polarity of the battery connected to the incoming trunk when the calling exchange trunk is connected thereto at the operators position and to restore the normal polarity of the battery when a finder switch is connected thereto, means at the operators position jointly responsive to the connection of said dial to the automatic exchange trunk and the restoration to normal polarity of said exchange battery to actuate said signal device as 'an indication to the operator that the automatic exchange is conditioned to receive dial'pulses, means for transmitting supervisory signals over said calling exchange trunk responsive to a reversal from normal of the automatic exchange battery, and other means to prevent transmission of said supervisory signals over said calling trunk until said dial has been disconnected from said automatic exchange trunk.

3. In a telephone exchange system, an operators position, a calling trunk incoming to said position, trunks between said position and said automatic exchange, switching means at said position for connecting said calling trunk to any one of said trunks-to the automatic exchange, finder switches at said automatic exchange fewer in number than said trunksterminating thereat, said automatic exchangebeing arranged to reverse the normal polarity of the battery supply thereat to any one of said trunks responsive to connection of said calling trunk thereto at the operators position, and to restore said battery supply polarity to normal when a finder switch attaches itself to the trunk, a dial and an associated signal device at said position, means for connecting said dial and associated signal device to any one of said trunks to the automatic exchange, means at said position jointly responsive to connection of said dial and signal device to any one of said trunks to the automatic exchange which is connected to said calling trunk and to a restoration of the normal battery polarity thereto, to actuate said signal device, and means in each automatic exchange trunk at said position for controlling the transmission of supervisory signals over a connected calling trunk responsive to batteryreversal from normal thereover, and means for preventing transmission of such supervisory signals until said dial has been connected and disconnected from the automatic exchange trunk.

4. In a telephone system, an operators position, an automatic exchange, trunks therebetween, a calling trunk terminating at said position and adapted to be connected to any one of said trunks to the automatic exchange, finder switches at said automatic exchange fewer in number than said trunks, said automatic exchange being arranged to reverse the normal polarity of the battery supplied to any one of said trunks when it is connected, at said position, to said calling trunk, and when a finder switch is brought into engagement therewith to restore said battery supply polarity to normal, a dial and an associated signal device at said position, means for connecting said dial to any one of said trunks and means responsive to the restoration to normal polarity of the trunk battery for actuating said signal device.

5. In a telephone system, a first exchange, an operators position, an automatic exchange, a first trunk extending between said first exchange and said position, a second trunk between said position and said automatic exchange, switching means at said position for connecting said first and second trunks, an impulse device at said position and means independent of said switching means for connecting said device to the second trunk, means for reversing the normal polarity of the battery supplied to said second trunk at the automatic exchange responsive to the interconnection of the first and second trunks and for restoring said battery polarity to normal when said automatic exchange is ready to receive control impulses, means at said position for transmitting a signal over said first trunk responsive to a battery reversal received over said second trunk, and means for preventing transmision of said signals over said first trunk until said impulse device has been connected and disconnected from said second trunk.

6. In a telephone system, an automatic exchange having trunks incoming thereto, trunk finder switches thereat fewer in number than said incoming trunk, said automatic exchange being arranged to reverse the normal polarity of the battery supplied to any trunk when seized at the outward end, a calling exchangaan intermediate operators position, a trunk between said calling exchange and the operators position, outgoing terminals at said automatic exchange trunks at said position, switching means at said position for connecting said calling exchange trunk to the outgoing terminals of one of said trunks to the automatic exchange, a supervisory bridge in the automatic trunk at the position adapted when closed to control a supervisory device at the calling exchange over the respective trunk, polarized means in the automatic exchange trunk at the position responsive to a reversal from normal polarity of the trunk battery at the automatic exchange for partially closing the respective bridge, an operators dial, means independent of said switching means for connecting said dial to the automatic exchange trunk, and means for completing closure of said bridge when said trunk battery is reversed, said means being responsive to the connection and subsequent disconnection of said dial from said automatic trunk.

7. In a telephone system, first and second exchanges, a first trunk for extending calls from said first to said second exchange, an automatic exchange, a second trunk between said second exchange and the automatic exchange, switching means at the second exchange for connecting said first to said second trunk line, an impulse device at said second exchange and means inde pendent of said switching means for connecting said device to the second trunk, supervisory means at said first exchange, a supervisory bridge circuit in said second trunk at the second exchang for controlling said supervisory means, said automatic exchange being arranged to transmit current of one polarity over said second trunk until the switches thereat are ready to receive control impulses, to reverse the polarity of said current when said switches are in readiness to receive impulses, and to again reverse the current when the called subscriber answers, means at said second exchange controlled by the polar ity of current transmitted from said automatic,

exchange for controlling said supervisory bridge, means responsive to the connection of said first trunk to said second trunk for disabling said supervisory bridge, and other means responsive to the connection and subsequent disconnection of said dial for enabling said bridge for closure in response to reversals of battery polarity over said second trunk.

8. In a telephone system, first'and second operators positions, a first trunk line for extending a call from the first to the second position and terminating at said second position in a cord and plug, an automatic exchange, a second trunk line terminating in a jack at the second position for extending the first trunk line from the second operators position to the automatic exchange, a dial jack at the second position associated with said second trunk line, an operators dial cord including a dial at the second position adapted to be connected to said dial jack for controlling the extension of said second trunk through said automatic exchange, a supervisory bridge circuit at said second position associated with said second trunk adapted when closed to control a supervisory device at the first operators position, said automatic exchange being so arranged that when said first and second trunks are connected, the polarity of the battery connected to the trunk at the automatic exchange will be in such a direction as to tend to close said bridge until a finder link is connected to the second trunk at which time the battery polarity will be reversed to tend to open said bridge, other means responsive to connection of said first of said second trunks for disabling said bridge and still other means responsive to the connection and subsequent disconnection of said dial to said second trunk to condition said bridge for closure under control of said trunk battery.

HORACE W. ULRICH. 

